The prime objective of this project is to develop an understanding of the fundamental chemistry of metal ions utilized in radioimmunotherapy, especially lead and bismuth. To accomplish this objective, we need to learn the coordination chemistry of metal ions, in particular, their kinetic and thermodynamic behaviors in solution. This information can then be used to develop radiolabeled antibody systems for use in therapy. Substantive progress was made on a project to label antibodies with Bi- 2l3. A column separation method was used to elute the alpha-emitting radionuclide, Bi-213, from an Ac-225 generator. Separation was done on a 150 mm3 column of MP-50 resin with the acids HI or HCl or both. To assay the complexation behavior of Bi-213, thin-layer chromatography was used with micromolar amounts of DTPA complexing ligand. Radiolabeling was done with the B3 monoclonal antibody (mAb) of the novel ligand CHX-B DTPA. The optimal results to-date are 38 microcuries (76%) of 50 microcuries Bi-2l3 incorporated into the mAb conjugate. The final specific activity was 0.24 microcurie/microgram.